This information applies to the latest version
The new compression is perceptually lossless.
This means: There are minimal mathematical deviations at the pixel level. However, these are not perceivable to the human eye, even under intensive image editing.
The compression was specifically developed and validated for RAW image data. It reduces only information that, from a perceptual point, does not contribute to visible image quality.
The result: About four times smaller files with unchanged perceptual image quality.
A detailed technical whitepaper on the underlying technology will be published online shortly.